\(\left(2x-1\right)\left(1+2x\right)-3\left(x-3\right)^2-\left(2+x\right)^2\)

\(=\left(2x-1\right)\left(2x+1\right)-3\left(x^2-6x+9\right)-\left(4+4x+x^2\right)\)

\(=4x^2-1-3x^2+18x-27-4-4x-x^2\)

\(=14x-32\)

Phần b ,c giải phương trình??

\(\left(2x-3\right)^2+\left(3-x\right)^2+2\left(3-x\right)\left(2x-3\right)=5\)

\(\Leftrightarrow\left(2x-3\right)\left(2x-3+2\left(3-x\right)\right)+\left(3-x\right)^2=5\)

\(\Leftrightarrow\left(2x-3\right)\left(2x-3+6-2x\right)+\left(3-x\right)^2=5\)

\(\Leftrightarrow3\left(2x-3\right)+9-6x+x^2=5\)

\(\Leftrightarrow6x-9+9-6x+x^2=5\)

\(\Leftrightarrow x^2=5\)

\(\Leftrightarrow x=\pm\sqrt{5}\)

\(\left(x+5\right)\left(5-x\right)+\left(2x-1\right)^2-\left(3x-1\right)\left(x+2\right)-7=0\)

\(\Leftrightarrow\left(5-x\right)\left(5-x\right)+4x^2-4x+1-\left(3x^2+6x-x-2\right)-7=0\)

\(\Leftrightarrow25-x^2+4x^2-4x+1-3x^2-6x+x+2-7=0\)

\(\Leftrightarrow21-9x=0\)

​\(\Leftrightarrow9x=21\)​

\(\Leftrightarrow x=3\)

đặt A=1+1/2 mu2+1/3 mu2+1/4 mu2+....+1/100 mu2

đặt B=1/2.3+1/3.4+...+1/99.100

=1/1.2+1/2.3+1/3.4+...+1/99.100

=1-1/2+1/2-1/3+...+1/99-1/100

=1-1/100<1 (1)

Mà 1<2(2)

A =1/1+1/2.2+1/3.3+...+1/100.100<1-1/2+1/2-1/3+...+1/99-1/100 (3)

từ (1),(2),(3) =>A<2

ủng hộ nhé

đề yêu câu ftinhs hay tính nhanh Đoàn Đức Hiếu cho nhok cày GP nè

a) \(\left(\dfrac{2}{3}\right)^3.\left(\dfrac{-3}{4}^2\right).\left(-1\right)^5\)

\(=\dfrac{8}{27}.\dfrac{9}{16}.\left(-1\right)\)

\(=\dfrac{1}{6}.\left(-1\right)\)

=\(\dfrac{-1}{6}\)

b) \(\left(\dfrac{2}{5}\right)^2.\left(\dfrac{-5}{12}\right)^2\)

\(=\dfrac{4}{25}.\dfrac{25}{144}\)

\(=\dfrac{1}{36}\)

\(\frac{3.8\left(-14\right)}{42.35}\)

\(=\frac{3.2.4.\left(-1\right).7.2}{2.3.7.5.7}\)

\(=-\frac{8}{35}\)

(3/7)² . (-7)⁴

= 3²/7² . 7⁴

= 3² . 7²

= 21²

= 441

\(\left(\dfrac{3}{7}\right)^2\cdot\left(-7\right)^4\)

\(=\dfrac{3^2}{7^2}\cdot7^4\)

\(=\dfrac{3^2\cdot7^4}{7^2}\)

\(=3^2\cdot7^2\)

\(=\left(3\cdot7\right)^2=441\)